Based on recent research, it is observed that the cumulative losses of the upstream process safety incidents in the last 40 years (1972-2011) are close to USD 7.3 Billion and these incidents occurred due to failure of multiple safety barriers. The disastrous consequences of Chongqing sour gas well blowout (USD 10 million and 243 fatalities) were attributed to the failure of safety barriers. To understand the failure of the safety barriers, the variables impacting barrier performance were studied. Initially, nineteen (19) variables were identified based on a cross-industry literature review. Expert interviews were conducted with fifteen (15) drilling and safety experts to refine the variables specific to onshore gas drilling operations. Expert interviews validated seventeen (17) variables from the cross-industry literature review and added eight (8) variables specific for onshore gas drilling operations. From a consolidated list of twenty five (25) variables, seven (7) factors have been identified through an Exploratory Factor Analysis method. The identified factors were validated by mixed group of professionals from the onshore gas drilling industry through a workshop and obtained an average rating of 4.8 out of 5. The current paper focuses on identifying factors which would aid in the evaluation of safety barrier performance. These factors could be considered while building future predictive risk models based on safety barrier performance. (C) 2017 Elsevier Ltd. All rights reserved.